This PDF file contains the front matter associated with SPIE Proceedings Volume 6552, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

There is an increasing need for the generation of mid-infrared radiation in the 3 to 5-micron region especially in the absorption minima of the atmospheric windows. Recent progress in heat seeking detector technology, operating in these atmospheric windows, make it necessary to develop compact and reliable mid-infrared laser systems that can be installed in airborne platforms. Future DIRCM systems will be equipped with high repetition rate/low energy per pulse lasers as well as low repetition rate/high energy per pulse lasers. We report on the development of a Tm:YLF-fiber laser (1.908 &mgr;m) pumped Ho:YAG (2.09 &mgr;m) high energy laser system with pulse energies up to 90 mJ at pulse lengths close to 20 ns and operating at 100 Hz. Using single mode fiber lasers as end-pumped sources for the master-oscillatorpower- amplifier (MOPA) system almost diffraction limited beam quality resulted. The frequency conversion into the 3 to 5-micron region is performed with a zinc germanium phosphide (ZGP) crystal in a linear or ring resonator. Propagation of the mid-infrared laser beam through moderate turbulent atmosphere will be simulated numerically using phase screens and Fresnel transformation.

Lawrence Livermore National Laboratory (LLNL) has been developing compact solid state lasers since the 1990's. One of the first lasers to be developed utilized flashlamp pumped architecture and neodymium glass as the laser gain media. In the early 2000's, a diode pumped version of the original flashlamp pumped laser was designed and built, responding to the requirements that a laser system for the military be compact in both size and weight while creating significant power (~100 kW) for the missions envisioned. This paper will discuss the evolution of solid state lasers at LLNL and provide a glimpse into the types of capabilities that could be achieved in the near future.

The material in which a volume Bragg grating is made will always have some absorption at the grating's design wavelength. Thus, when exposed to a high power laser beam the grating will absorb some power, be heated such that a temperature gradient is formed and, consequently, become distorted. We developed an accurate model to calculate the reflection of a high power laser beam by a volume Bragg grating that experiences such distortion. We used the beam propagation method (BPM) to calculate the laser beam propagation in the grating numerically, and the BPM calculations are iterated to account for the counter propagation of the laser beam in the volume Bragg grating. We devised a new method to assure convergence in the iteration of the BPM calculations when the grating diffraction strength is very large. We also established a new formulation of the wave equation to include the grating period distortion in the BPM formulation. The surface distortion and temperature induced background index change are also included in the model. This model has been validated to be correct and very accurate. We applied it to calculate the reflection of a high power laser beam by a distorted volume Bragg grating which has large diffraction strength. Our calculation shows that a small amount of grating structure distortion could introduce significant changes of both the phase and intensity patterns of the reflected laser beam. Understanding such changes is critical to the application of volume Bragg grating to high power laser systems.

We present lasing results of a SiC face cooled 4% Nd:YAG ceramic in an unstable cavity mode configuration (slope efficiency 35%) under quasi-CW pump conditions. This work demonstrates the first time lasing of a high temperature bonded, anti-reflection (AR) coated bonded SiC/Nd:YAG assembly. Finite Element Analysis (FEA) modeling of the temperature, stress, thermal lensing and polarization loss of the SiC/Nd:YAG stack under lasing conditions are presented.

The thermal conductivity of CVD diamond with about 18-25 W/cm.K at room temperature is one of the properties that makes diamond a unique material. Since thermal management of solid state lasers becomes increasingly difficult when scaling up to high average power, CVD diamond is an ideal heat spreader to conduct heat away to a heat sink. At the same time, diamond is transparent between 230nm and the far infrared, with two-photon absorption bands between 2.5 and 6 μm. Adhesive-Free Bonding (AFB®) of CVD diamond sheet has been demonstrated to be possible because Van der Waals attractive forces constitute the principal bonding mechanism of AFB® composites. The coefficient of thermal expansion of CVD diamond is with 0.8 - 1.0 x 10^-6/°C much lower than any of the common solid state laser media, with YAG being about 8.2 x 10^-6/°C. The non-localized nature of Van der Waals bonds allows almost perfect stress equilibration without delamination, while any other bonding technique would be expected to result in highly stressed composites. Bonding mechanisms, experimental observation of stress relief and parameters for successful AFB® CVD diamond/ single crystal composites at the interface will be reported, with relevance for disk, slab and waveguide solid state laser geometries at ambient and cryogenic temperature.

We report the first demonstration of polycrystalline Nd:YAG (Y₃Al₅O₁₂), and Nd-doped YAG single crystal with almost perfect pore-free structure by advanced ceramic processing. The laser conversion efficiency of pore-free polycrystalline Nd and Yb doped ceramics is extremely high, and their optical qualities are comparable to that of commercial high quality Nd:YAG single crystal. We have succeeded also in the fabrication of Nd:YAG single crystal, which can be used for laser oscillation, by solid-state reaction method. Laser oscillation efficiency was very low when pores were remained inside single crystal, however the laser oscillation efficiency of pore-free Nd:YAG single crystal was slightly higher than that of polycrystalline Nd:YAG ceramics having high optical quality. From this fact, it was recognized that the optical scattering occurs mainly at the residual pores inside the Nd:YAG ceramics, and the scattering at the grain boundary is very little. In addition, we confirmed that Nd heavily-doped YAG single crystal can be fabricated by sintering method. We have demonstrated the fabrication of composite ceramic with complicated structures without the needs of precise polishing and diffusion bonding. Advanced ceramic processing, which enables design flexibility of laser element, presented in this work is important in the development of high performance laser (high efficiency, high beam quality and high output energy etc.) Moreover, we have recently developed polycrystalline ceramic fiber laser first in the world, and achieved over 8W output per unit length of the fiber.

Optical quality ceramic Yttrium Aluminum Garnet (YAG, Y₃Al₅O₁₂) materials for high power solid state lasers are being developed at Raytheon. The remaining challenge for ceramic gain materials is elimination of residual absorption and scattering centers. At Raytheon, significant progress has been achieved in the optical quality improvement, scale-up, and demonstration of laser quality Yb, Nd, and Er doped ceramic YAG materials. This communication presents Raytheon's current development status in ceramic YAG fabrication and doped ceramic YAG material characteristics.

A novel method of making a line tunable, visible and near ultraviolet, laser source is proposed and demonstrated. It requires only a single laser and 2 nonlinear crystals. It can produce outputs with wavelengths that cover much of the spectrum from 0.26 to 0.67 &mgr;m.

In this paper we discuss a CW Yb:YAG cryogenic laser program that has resulted in the design and demonstration of a novel high power laser. Cryogenically-cooled crystalline solid-state lasers, and Yb:YAG lasers in particular, are attractive sources of scalable CW output power with very high wallplug efficiency and excellent beam-quality that is independent of the output power. This laser consists of a distributed array of seven highly-doped thin Yb:YAG-sapphire disks in a folded multiple-Z resonator. Individual disks are pumped from opposite sides using fiber-coupled ~ 30W 940nm pump diodes. The laser system we have constructed produces a near-diffraction-limited TEM₀₀ output beam with the aid of an active conduction-cooling design. In addition, the device can be scaled to very high average power in a MOPA configuration, by increasing the number and diameter of the thin disks, and by increasing the power of the pump diodes with only minor modifications to the current design. The thermal and optical benefits of cryogenically-cooled solid-state lasers will be reviewed, scalability of our Yb:YAG cryogenic laser design will be discussed, and we will present experimental results including output power, slope and optical-optical efficiencies, and beam-quality.

Recent advances in compact solid sate lasers for laser designation, eye-safe range finding and active imaging are described. Wide temperature operation of a compact Nd:YAG laser was achieved by end pumping and the use of multi-&lgr; diode stacks. Such lasers enabled construction of fully operational 4.7 lb laser designator prototypes generating over 50 mJ at 10-20 Hz PRF. Output pulse energy in excess of 100 mJ was demonstrated in a breadboard version of the end-pumped laser. Eye-safe 1.5 &mgr;m lasers based on flash-pumped, low PRF, Monoblock lasers have enabled compact STORM laser range finders that have recently been put into production. To achieve higher optical and electrical efficiency needed for higher PRF operation, Monoblock lasers were end-pumped by a laser diode stack. Laser diode end-pumped Monoblock lasers were operated at 10-20 Hz PRF over a wide temperature range (-20 to +50^oC). Compared with bulk compact solid state lasers, fiber lasers are characterized by lower pulse energy, higher PRF's, shorter pulses and higher electrical efficiency. An example of fiber lasers suitable for LIDAR, and atmospheric measurement applications is described. Eye-safe, low intensity diode pumped solid state green warning laser developed for US Army checkpoint and convoy applications is also described.

We report an eyesafe diffraction-limited single-frequency 1617 nm Er:YAG laser transmitter for coherent laser radar applications. The transmitter utilizes a master oscillator/power amplifier architecture, enabling the production of high peak power output. The pulsed oscillator is Q-switched and cavity-dumped, resulting in a 1.1 ns pulsewidth. The pulsed oscillator is injection-seeded by a commercial 1617 nm CW distributed feedback laser diode, resulting in single longitudinal mode output. The oscillator and amplifier are directly pumped into the Er:YAG laser upper state by commercial diode-pumped CW 1533 nm Yb,Er-doped fiber lasers. The injection-seeded pulsed oscillator produces an average output power of 2.2 W at 10 kHz pulse repetition frequency (PRF) with a pulsewidth of 1.1 ns (0.20 MW peak power) with a beam quality 1.1 times the diffraction limit. The oscillator has a slope efficiency of 47% in the CW mode, and a conversion efficiency of 85% from CW mode to injection-seeded pulsed mode. The power amplifier produces 20 W in the CW mode with an optical-to-optical conversion efficiency of 34% and a beam quality 1.1 times the diffraction limit, and 6.5 W in the pulsed mode at 10 kHz PRF with 1.1 ns pulsewidth (0.59 MW peak power).

Erbium doped YAG is an intriguing laser material which lases directly at 1645nm when pumped at either 1473nm or 1532nm, all of which are in the eye-safe band. However, a laser made from this material is not particularly straightforward to design. Er:YAG is a quasi-three-level system, which leads to strong temperature dependence. Perhaps more importantly, a strong up-conversion process, which is dopant concentration dependent, effectively produces a pump intensity dependence in the saturation intensity and other laser parameters. We present a detailed study of the absorption coefficient and the gain as a function of the pump intensity, dopant concentration and crystal temperature. The results of this study will allow us to optimally design the laser.

Significant performance improvement of the Er(0.5%):YAG diode pumped solid state laser (DPSSL) has been achieved by pump diode spectral narrowing via implementation of an external volumetric Bragg grating (VBG). Without spectral narrowing, with a pump path length of 15 mm, only 37% of 1532 nm pump was absorbed. After the VBG spectral narrowing, the absorption of the pumping radiation increased to 62 - 70%. As a result, the incident power threshold was reduced by a factor of 2.5, and the efficiency increased by a factor of 1.7, resulting in a slope efficiency of ~23 - 30%. A maximum of 51 W of CW power was obtained versus 31 W without the pump spectrum narrowing. More than 180 mJ QCW pulse output energy was obtained in a stable-unstable resonator configuration with a beam quality of M² = 1.3 in the stable direction and M² = 1.1 in the unstable direction. The measured slope efficiency was 0.138 J/J with a threshold energy of 0.91 J.

Ultra-low quantum defect operation Er lasers are discussed. Power scaling demonstration has shown promise for high efficiency Er:crystal laser operation.

Efficient ultra-low-photon-defect resonantly diode-pumped Er:YAG cryogenically-cooled laser is demonstrated for the first time. Quasi-CW diode pumping by InGaAsP/InP 10-diode bar stack (without spectral narrowing) was implemented. Laser performance at ~80°K in this first experiment was found to be 71.5% efficient (output power versus power absorbed in the cavity mode, slope). Er:YAG laser output variations with the gain medium temperature was investigated. Maximum quasi-CW power of ~65 W was achieved by optimization the gain medium operating temperature. and to photon number splitting attacks, thus resulting in a high efficiency in terms of distilled secret bits per qubit. After having successfully tested the feasibility of the system [3], we are currently developing a fully integrated and automated prototype within the SECOQC project [4]. We present the latest results using the prototype. We also discuss the issue of the photon detection, which still remains the bottleneck for QKD.

We describe a three-channel, spectrally beam combined (SBC), 1-&mgr;m fiber laser that features a SBC power combining efficiency of 93%, versatile master-oscillator, power-amplifier (MOPA) fiber channels with up to 260 W of narrowband, polarized, and near-diffraction limited output, and currently produces 522 W of average power with a dispersed (non-dispersed) beam quality at 522 W of 1.18x (1.22x) diffraction limited. To our knowledge, these results represent the best combination of output power and beam quality achieved by SBC to date.

We have developed a fiber laser system capable of producing over 100W of average power. We have achieved 1.5mJ/pulse/fiber resulting in peak powers in excess of 2MW with 0.6ns pulses and near diffraction limited beams. In another fiber, we have achieved over 0.5mJ/pulse with pulses of 700ps exceeding 500kW of peak power in polarization maintaining Ytterbium doped fiber. In both cases, wall-plug efficiencies, excluding cooling of the pump diode lasers, in excess of 15% were also achieved. The system we have developed is based in an all fiber design except for the last high peak power isolator requiring free space optics. With the advent of such a component, a scalable 1.5MW/arm all fiber laser system is proven to be possible.

A novel side coupling technique between two multimode high NA fibers is described. The technique is used to efficiently pump fiber lasers and amplifiers by low brightness fiber coupled pump diodes. With the presented technique, identical multimode fibers with 0.46NA and core diameters extending from 125&mgr;m to 400&mgr;m, can be coupled together, and provide pump coupling efficiency of >90%. Direct coupling to a rare-earth doped fiber is possible. In this configuration one fiber is used as the pump guiding fiber and the second fiber is the rare-earth doped double clad fiber. By utilizing the presented pump coupling technique, highly efficient, rugged and low cost short pulse and CW all-fiber lasers were implemented, with average output power extending to 300W and peak power of 600kW.

Coherent Laser Radar is a powerful remote sensing tool, which can be applied to range-finding, target discrimination, vibrometric monitoring, air pollution monitoring, aircraft wake-vortex and clear-air turbulence analysis. A high power, highly efficient, near diffraction limited and highly reliable pulsed coherent laser source is a key sub-system required in a coherent Lidar sensor. When humans are involved, eye safe laser emission is also typically required. Therefore a highly efficient fiber laser system based on a coherent Master-Oscillator followed by a chain of Erbium (EDFA) and Erbium co-doped with Ytterbium fiber amplifiers (EYDFA) is ideally suited for this application suite. In this paper, we are presenting an all polarization-maintaining fiber architecture and experimental results on such a high peak power fiber laser system allowing for versatile modulation strategies at a wavelength of 1563nm commensurate with a clear atmospheric transmission window and eye-safe operation. The system is constituted by three amplification stages, all based on Polarization-Maintaining fiber. With 660ns and 20Kpps, over 500W peak power pulses have been experimentally demonstrated with near diffraction limited performance with this all PM fiber system.

We have investigated room temperature fluorescence in the 500-900nm spectral region from high optical quality, polished and uncoated KTP crystals from three different commercial vendors. The crystals were all cut into 5mm x 5mm x 5mm cubes with their dielectric axes along the cube edges. The pump source was a tripled Nd:YAG laser operating at 355nm and 7mJ energy having 3ns pulse width and 100Hz pulse repetition rate. Samples from two vendors showed low fluorescence of similar magnitude while samples from the third vendor showed nearly two orders of magnitude higher value in the peak fluorescence near 800nm. In addition, all samples showed a weaker secondary fluorescence band peaking near 600nm. A low fluorescence sample from one of the vendors also showed typical "gray tracking" at these pump radiation conditions. We have also measured lifetimes of 2.9±0.7 µs and 4.9±0.1 µs for the centers responsible for fluorescence near 845nm and 595nm respectively in the KTP sample showing highest fluorescence and "gray tracking" in this group of samples. The manufacturing processes used to produce high optical quality and low fluorescence KTP materials are proprietary to the commercial vendors and were not provided. Possible origin and sources of fluorescence in these materials are discussed consistent with those published in the literature.

Fiber lasers create unique opportunities for creating high energy lasers. The distributed gain and heat deposition, and the flexible resonator provide the means for scaling to high powers. In addition and perhaps more valuable is the idea that fiber lasers allow the creation of an extensible architecture: an architecture where the individual components can be researched, designed, improved and replaced independently. In order to create sources at power levels over 10kW in volumes less than 1 cu. ft. weighing less than 50lbs at costs under $1 per Watt of laser output. Serious consideration first needs to be given to the underlying architecture of choice. In this presentation, several architectural constraints along with competing approaches will be presented. Preliminary results from high brightness fiber coupling designs and simulations will also be discussed.

Beam walk-off in uniaxial and biaxial crystals occurs when the phase normal of the propagating electromagnetic wave deviates from the direction of the Poynting vector. This beam walk-off limits frequency conversion efficiency and restricts the OPO tuning range. The beam walk-off angle in nonlinear single crystals can be alleviated by bonding similar non-linear crystals rotated by 180° with respect to each other. An even number of twisted twins of single crystals is formed that is stress-free and has negligible loss at the AFB® (Adhesive-Free Bond) interfaces. Since no adhesive is employed and the bonding force consists primarily of Van der Waals attractive forces, there is no adverse effect or absorption at the bond interface. The theory of walk-off angles as a function of orientation for uniaxial and biaxial crystals is derived. Correcting beam walk-off by producing an AFB® composite configuration results in more efficient frequency conversion and thereby allows the generation of higher power output of frequency converted radiation for a given input power. Beam correction is demonstrated experimentally for zinc germanium phosphide (ZGP) as representative of a uniaxial nonlinear crystal, and on biaxial KTP crystals. AFB® composites of ZGP with inactive ends of gallium phosphide have been produced in an effort to further improve damage resistance of a ZGP optical parametric oscillator for frequency conversion into the mid-IR range.

Recent progress in transition metal doped II-VI semiconductor materials (mainly Cr²⁺:ZnSe) makes them the laser sources of choice when one needs a compact system with continuous tunability over 2-3.1 &mgr;m, output powers up to 2.7 W, and high (up to 70%) conversion efficiency. The unique combination of technological (low-cost ceramic material) and spectroscopic characteristics make these materials ideal candidates for "non-traditional" regimes of operation such as microchip and multi-line lasing. This article reviews these non-traditional Cr-doped mid-IR lasers as well as describes emerging Fe²⁺:ZnSe lasers having potential to operate at room temperature over the spectral range extended to 3.7-5.1 &mgr;m. In addition to effective RT mid-IR lasing transition metal doped II-VI media, being wide band semiconductors, hold potential for direct electrical excitation. This work shows the initial steps towards achieving this goal by studying Cr²⁺, Co²⁺, and Fe²⁺ doped quantum dots. We have demonstrated a novel method of TM doped II-VI quantum dots fabrication based on laser ablation in liquid environment. TM doped II-VI quantum dots demonstrated strong mid-IR luminescence. It opens a new pathway for future optically and electrically pumped mid-IR lasers based on TM doped quantum confined structures.

Real time detection and identification of explosives at a standoff distance is a major issue in efforts to develop defense against so-called Improvised Explosive Devices (IED). It is recognized that the only technique, which is potentially capable to standoff detection of minimal amounts of explosives is laser-based spectroscopy. LDS technique belongs to trace detection, namely to its micro-particles variety. We applied gated Raman and time-resolved luminescence spectroscopy for detection of main explosive materials, both factory and homemade. Raman system was developed and tested by LDS for field remote detection and identification of minimal amounts of explosives on relevant surfaces at a distance of up to 30 meters.

We demonstrate an Er-fiber-laser-pumped, CW, high-power, single-longitudinal-mode Cr²⁺:ZnSe laser, tunable in the 2- 3 &mgr;m spectral region. The laser is operating in a single longitudinal mode regime with a linewidth of 80-130 MHz over a 120 nm tuning range around 2.5 &mgr;m, and delivers up to 150 mW of output power. The laser design is very compact and is based on Kogelnik/Littman cavity configuration with the total optical length of the folded cavity of 10 cm. The narrow-linewidth output spectrum can be quickly scanned over a 10 nm spectral range with a repetition rate of 220 Hz by a piezo-controlled tuning mirror which allows for an extremely fast wavelength tuning of the output spectrum over a large number of absorption spectral lines of trace gases of interest. As a test experiment, we performed a Dopplerlimited- resolution intracavity laser absorption spectroscopy of ro-vibrational transitions of the &ngr;₃ and &ngr;₁ bands of H₂O with minimum detectable absorption coefficient of ~3x10^-7 cm^-1, which corresponds to 9 parts per billion by volume water vapor detection limit. The laser is currently in active stage of development and its further optimization will allow for full 2-3 &mgr;m fast tuning range and Watt-level output powers. This laser is being designed as a seeding source for an OPG-OPA-based, highly sensitive trace-gas sensor system for real-time detection of gas traces of biological pathogens and explosives in the molecular fingerprint mid-IR spectral region of 2-10 &mgr;m.

Fiber-coupled systems based on broad-area multimode emitters require complicated optical trains in order to transform their poor quality output beam into a usable form. Recently, Nuvonyx has reported implementations of a single spatial mode, high-brightness laser diode bar with significantly improved beam quality. These laser bars represent a broad technology platform at the core of many Nuvonyx systems. The low output divergence of these devices enables efficient coupling into a 400 &mgr;m core, 0.22 numerical aperture fiber with a single focusing lens. Larger systems using stacks of high-brightness diode laser bars can achieve greater than 1.7 kW output from this same fiber size, corresponding to a power density level exceeding 1.4 MW/cm². The high-brightness bars reported here are compatible with techniques for achieving high spatial or spectral brightness. Using external feedback elements such as a volume Bragg grating, the output spectrum can be narrowed to less than 0.25 nm and is stabilized to dλ/dI = 4 pm/A and dλ/dT = 2 pm/°C. Using spectral beam combination, a single high brightness bar can be coupled into a 100 &mgr;m core, 0.22 NA fiber with approximately 90% efficiency.

We present recent advances in high power semiconductor laser bars and arrays at near infrared wavelengths including increased spectral brightness with internal gratings to narrow and stabilize the spectrum and increased spatial brightness with multimode and high power single mode performance. These devices have the potential to dramatically improve diode pumped systems and enable new direct diode applications.

We present recent advances in high power semiconductor laser bars and arrays at eye-safe wavelengths including increased spectral brightness with internal gratings to narrow and stabilize the spectrum. These devices have the potential to dramatically improve diode pumped Er:YAG systems and enable new direct diode applications.

Mid-infrared light emitters capable of room temperature continuous-wave (CW) operation are in demand for variety of applications ranging from medical diagnostics to missile countermeasures. Room temperature type-I quantum-well (QW) GaSb-based lasers, laser arrays and light emitting diodes operating in the spectral range from below 2 to over 3&mgr;m have been reported. The maximum CW output power from 1cm-wide 2.35&mgr;m linear laser array was 10 W, in quasi-CW operation (30 &mgr;s pulse, 300 Hz pulse repetition frequency) the maximum measured power is 18.5 W. In short pulse operation heating is negligible, and the light-current characteristics remains linear to beyond 20 W at 100 A.

Peak CW optical power from single 1-cm diode laser bars is advancing rapidly across all commercial wavelengths and the available range of emission wavelengths also continues to increase. Both high efficiency ~ 50% and > 100-W power InP-based CW bars have been available in bar format around 1500-nm for some time, as required for eye-safe illuminators and for pumping Er-YAG crystals. There is increasing demand for sources at longer wavelengths. Specifically, 1900-nm sources can be used to pump Holmium doped YAG crystals, to produce 2100-nm emission. Emission near 2100-nm is attractive for free-space communications and range-finding applications as the atmosphere has little absorption at this wavelength. Diode lasers that emit at 2100-nm could eliminate the need for the use of a solid-state laser system, at significant cost savings. 2100-nm sources can also be used as pump sources for Thulium doped solid-state crystals to reach even longer wavelengths. In addition, there are several promising medical applications including dental applications such as bone ablation and medical procedures such as opthamology. These long wavelength sources are also key components in infra-red-counter-measure systems. We have extended our high performance 1500-nm material to longer wavelengths through optimization of design and epitaxial growth conditions and report peak CW output powers from single 1-cm diode laser bars of 37W at 1910-nm and 25W at 2070-nm. 1-cm bars with 20% fill factor were tested under step-stress conditions up to 110-A per bar without failure, confirming reasonable robustness of this technology. Stacks of such bars deliver high powers in a collimated beam suitable for pump applications. We demonstrate the natural spectral width of ~ 18nm of these laser bars can be reduced to < 3-nm with use of an external Volume Bragg Grating, as required for pump applications. We review the developments required to reach these powers, latest advances and prospects for longer wavelength, higher power and higher efficiency.

We have developed a time dependent model for the eye-safe laser emission at 1.6&mgr;m, representing transitions from the manifolds 4I13/2 to 4I15/2 of trivalent Er-doped YAG (Y₃Al₅O₁₂). The model is based on a set of coupled first-order differential equations (rate equations) that describe the laser kinetics of this quasi-three level laser system. Also called zero-dimensional (0-D) equations, these equations are time only dependent with no spatial dimension dependency. The model is anchored to experimental results including the experimental Stark levels that are populated according to a Boltzmann distribution at room temperature. Emission cross section parameters are calculated using reciprocity methods from experimental absorption cross sections. A MATLAB code is written and the equations are solved numerically for output power and slope efficiency and threshold. The results are useful with significant progress towards predicting the published experimental laser data. This model can be optimized for its parameters such as output coupler reflectivity, ion concentration, etc and used for other hosts.

The thermal lensing effect in Nd:YAG laser rods at pumping by concentrated solar flux of Big Solar Furnace of the Scientific and Production Association "Physics-Sun"(Tashkent) is considered. For solving of the problem the computer model of the process was developed and the numerical experiments were performed.

We discuss major factors responsible for obtaining transparent Nd³⁺:YAG ceramic, a prospective material for laser applications. The relationship between the properties of starting nanopowders and the transmittance of specimens sintered at the different "ramp-soak" conditions was established by means of spectroscopic, structural, and electronic microscopy studies. It was found, that sample's transmittance (in some cases) depends on the duration of the holding time at the sintering stage. This result is promising for obtaining laser quality materials. It also contributes to basic understanding of the processes underlying fabrication of transparent laser ceramic.

This paper describes the structure and operation of a stable, fast-tuning, narrow-linewidth, all polarization-maintaining fibre ring laser using erbium-doped fibre as a saturable absorber. The optimum pump power for single-mode operation in the laser is identified. Laser output power is ~4.0mW at 1536nm for a pump power of 80mW, the polarization extinction ratio is 25.0dB, the SNR is larger than 60dB, the relative intensity noise is below -118dB/Hz at frequencies above 90kHz. The phase noise achieves −107dB at 1kHz while the modulation frequency of lasing optical frequency is 12.5kHz.

The information on the variety, nature and structure of the centers formed by the rare earths ions doped in the transparent laser ceramics of garnets and cubic sesquioxides, acquired from high-resolution spectroscopy and emission decay is analyzed. The quantum states (energy levels, transition probabilities) of several doping rare earth ions, their distribution at the available lattice sites, the interactions between ions, and energy transfer processes are also presented. It is inferred that from spectroscopic point of view these materials could substitute the melt-grown single crystals in construction of solid-state lasers and extend considerably their capabilities.

A conductively cooled laser diode package design with hard AuSn solder and CTE matched sub mount is presented. We discuss how this platform eliminates the failure mechanisms associated with indium solder. We present the problem of catastrophic optical mirror damage (COMD) and show that nLight's nXLT^TM facet passivation technology effectively eliminates facet defect initiated COMD as a failure mechanism for both single emitter and bar format laser diodes. By combining these technologies we have developed a product that has high reliability at high powers, even at increased operation temperatures. We present early results from on-going accelerated life testing of this configuration that suggests an 808nm, 30% fill factor device will have a MTTF of more than 21khrs at 60W CW, 25°C operating conditions and a MTTF of more than 6.4khrs when operated under hard pulsed (1 second on, 1 second off) conditions.